by Amelia Young
As floodwaters have flowed across eastern Australia this summer, they’ve been followed by a flood of calls for the construction of more, or bigger dams and water storage capacity.
To Mr Abbott, a dam can be all things to all people – “a flood mitigation device, a potential provider of zero emissions power, and a source of environmental flows in dry times as well as means of better water security for farmers.”
By the time the waters reached Victoria, federal environment minister Tony Burke and the new Victorian water minister Peter Walsh had both caught dam fever. Minister Burke announced a dam upgrade for Tamworth in NSW and said he’d welcome new dam proposals from the states.
The Victorian Coalition government announced feasibility studies for the expansion of water storage in the state’s north-east for town water supplies and in Gippsland for irrigation; and they won’t rule out the possibility of new dams in the future.
The calls for new dams or expanded water storage have generally been justified to capture all that excess water and save it for the next drought; and/or hold back all that water to prevent destructive floods.
In other words, proponents believe dams can both drought-proof and flood-proof Australia at the same time.
Amidst the rhetoric, it’s not hard to detect a desire for some good old-fashioned nation-building to tame the wild and mould Australia’s climate to our needs.
Right now, through the Murray-Darling Basin Plan, we’re collectively attempting to grapple with the effects of 100 years of dam-building.
There are already more than 30 major dams, and over 4,000 weirs in the Murray-Darling Basin. Since the 1880s they’ve been built in a quest to turn ‘water into gold’ by transforming Australia’s unruly stop-start river systems into regular, reliable streams like we’d been used to back in Europe. The amazing engineering feat of locks, weirs, pipes, dams, channels and wheels has changed the face of the Murray River and its floodplains, forever. The consequences for the environment have been disastrous.
Seasonally, the rivers’ natural flow patterns have been turned on their head. In summer, ecosystems adapted to lower flows and warm water are assailed by dams sending out high flows of cold water. Then in winter, when our environment is primed for floods, dams hold back the rainfall and keep river levels artificially low.
As ecologist Dr Paul Humphries points out, this means that "our rivers – and the animals and plants that live in them have been exposed to massive climate change for more than 100 years."
When water is released from the depths of a dam, its temperature can be 5-15 degrees Celsius colder than water running over or around a dam wall. The temperature effects are measurable up to 300 kilometres downstream. Native fish that require warmer water for breeding, such as the Silver Perch or the Macquarie Perch, are threatened and declining in numbers.
Dams and weirs also create barriers preventing fish from moving up and downstream for feeding, breeding and spawning. In Victoria, nine native fish are at risk of extinction due to the presence of weirs.
Australia's natural environment thrives on a flood. In fact some plants, birds and animals need them to survive. The threatened Plumed Egret only nests and breeds in flooded River Red Gum forested wetlands and the endangered Murray Cod only spawns during floods.
The plethora of dams and weirs in the Murray-Darling do what they’re designed to – capture water for later use. But as we’ve seen this year, the really big floods still get through.
It’s amazing how quickly the floods are washing away the public’s memory of the drought that savaged the mighty Murray and its tributaries for 13 long years.
During that drought, dams and irrigation deprived rivers and wetlands of life-giving small floods. The result was dying river red gums, stagnant swamps, and a massive drop in water-bird numbers.
Unless something changes in the way we manage our rivers, they will continue to be deprived of a fair share of water and the same thing will happen the next time drought strikes.
If using dams to try to control Australia’s boom-bust climate was a bad idea before, it’s an even sillier ambition to resurrect when faced with the onslaught of climate change.
Given the scientific predictions for a hotter, drier future, interspersed with more extreme flooding events, a flurry of dam-building is a short-sighted and reactive policy response. To manage the worst flood events, dams would have to be over-engineered and stand empty most of the time, poised ready to capture a rare and unpredictable flood.
By contrast, if the aim is to provide a secure water supply even during droughts, dams would need to be kept as full as possible for as long as possible, if it rains enough to fill them.
Even worse, new dams will compound the damage already done to river systems, just when we need to be strengthening the resilience of our natural environment to withstand greater climatic extremes.
The simple truth is that for too long we’ve taken out too much water from our rivers. To restore our rivers to health, the new national plan must set aside a fair share of available water for our rivers, in both wet and dry years.
The science shows that rivers in the Murray-Darling Basin need up to 7,600 billion litres of water secured through the plan, so they can be healthy for the long-term and support us all – and that’s under conservative climate change scenarios.
As always, the challenge is to live within natural limits and accept the need to adapt to our variable climate.
This opinion piece was published in the Climate Spectator on Friday, 18 February 2011